From: Alexei Starovoitov <redacted>
Date: Fri, 30 Nov 2018 13:58:20 -0800

On Thu, Nov 29, 2018 at 07:32:41PM -0800, David Miller wrote:

quoted

+/* If BPF_F_ANY_ALIGNMENT is used in BPF_PROF_LOAD command, the
+ * verifier will allow any alignment whatsoever.  This bypasses
+ * what CONFIG_EFFICIENT_UNALIGNED_ACCESS would cause it to do.

I think majority of user space folks who read uapi/bpf.h have no idea
what that kernel config does.
Could you reword the comment here to say that this flag is only
effective on architectures and like sparc and mips that don't
have efficient unaligned access and ignored on x86/arm64 ?

Ok.

quoted

+	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) &&
+	    (attr->prog_flags & BPF_F_ANY_ALIGNMENT) &&
+	    !capable(CAP_SYS_ADMIN))
+		return -EPERM;

I guess we don't want to add:
if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) &&
    (attr->prog_flags & BPF_F_ANY_ALIGNMENT))
        return -EINVAL;

so that test_verifier.c can just unconditionally pass this flag
on all archs ?

Right.

quoted

@@ -247,7 +249,11 @@ int bpf_verify_program(enum bpf_prog_type type, const struct bpf_insn *insns,
 	attr.log_level = log_level;
 	log_buf[0] = 0;
 	attr.kern_version = kern_version;
-	attr.prog_flags = strict_alignment ? BPF_F_STRICT_ALIGNMENT : 0;
+	if (strict_alignment)
+		prog_flags |= BPF_F_STRICT_ALIGNMENT;
+	if (any_alignment)
+		prog_flags |= BPF_F_ANY_ALIGNMENT;
+	attr.prog_flags = prog_flags;

instead of adding another argument may be replace 'int strict_alignment'
with '__u32 prog_flags' ?
and future flags won't need tweaks to bpf_verify_program() api.

Yeah the number of arguments are getting out of control, I'll do that.